1. Field of the Invention
The present invention relates to a liquid crystal display device.
2. Discussion of the Related Art
Until recently, display devices have typically used cathode-ray tubes (CRTs). Presently, much effort has been expended to develop various types of flat panel displays, such as liquid crystal display (LCD) devices, plasma display panels (PDPs), field emission displays, and electro-luminescence displays (ELDs), as substitutes for CRTs. Of these types of flat panel displays types, LCD devices have many advantages, such as high resolution, light weight, thin profile, compact size, and low power requirements.
In general, an LCD device includes two substrates that are spaced apart and facing each other with a liquid crystal layer interposed between the two substrates. The two substrates include electrodes that face each other such that a voltage applied between the electrodes induces an electric field across the liquid crystal layer. Alignment of the liquid crystal molecules in the liquid crystal layer changes in accordance with the intensity of the induced electric field to align with the direction of the induced electric field, thereby changing the light transmissivity of the LCD device. Thus, the LCD device displays images by varying the intensity of the induced electric field in respective pixel regions that make up the LCD device. Presently, a wide viewing angle is needed for LCD devices. A vertical alignment (VA) mode LCD device has these characteristics. The VA mode LCD device uses liquid crystal molecules having negative dielectric anisotropy and an alignment layer rubbed vertically.
FIG. 1 is a cross-sectional view illustrating a VA mode LCD device according to the related art, and FIG. 2 is a cross-sectional view illustrating alignment of liquid crystal molecules of FIG. 1.
Referring to FIG. 1, a VA mode LCD device 60 includes an array substrate B1, a color filter substrate B2, and a liquid crystal layer 14 between the two substrates.
The array substrate B1 includes gate and data lines (not shown) that cross each other to define a pixel region P and a thin film transistor T that is connected to the gate and data lines, on a first substrate 32. The thin film transistor T includes a gate electrode 30, a semiconductor layer 34, and source and drain electrodes 36 and 38. A pixel electrode 46 is disposed in the pixel region P and connected to the drain electrode 38. A gate insulating layer 32 is disposed on the gate electrode 30. A passivation layer 40 is disposed on the source and drain electrodes 36 and 38.
The color filter substrate B2 includes a black matrix 52 and a color filter layer on a second substrate 50. The color filter layer includes red (R), green (G) and blue (B) color filter patterns 54a, 54b and 54c in the corresponding pixel regions P. A common electrode 56 is disposed on the color filter layer. A rib 58 is disposed on the common electrode 56. The wide viewing angle is achieved using the rib 58.
Referring to FIG. 2, when an electric field is induced by the voltages applied to the pixel and common electrodes 46 and 56, the electric field near the rib 58 is distorted due to the rib 58. The distorted electric field is symmetrical with respect to the rib 58. The liquid crystal molecules 70 are also arranged symmetrically with respect to the rib 58, and first and second domains D1 and D2 are formed symmetrically with respect to the rib 58. Accordingly, light passing through the first and second domains D1 and D2 are compensated, thus color shift is reduced, and viewing angle is widened.
FIGS. 3A and 3B are cross-sectional views illustrating a method of fabricating the color filter substrate of FIG. 1.
Referring to FIG. 3A, a black matrix 52 is formed on a substrate 50 with a mask process. The black matrix 52 has an opening corresponding to a pixel region P. Red, green and blue color filter patterns 54a, 54b and 54c are formed in the corresponding pixel regions P with the corresponding mask processes.
Referring to FIG. 3B, a common electrode 56 is formed on the color filter patterns 54a, 54b and 54c. A rib 58 is formed on the common electrode 56 with a mask process.
Through the above processes, the color filter substrate is fabricated using five masks for the black matrix, the red, green and blue color filter patterns, and the rib.
Because the common electrode is formed directly on the color filter patterns, the common electrode has step portions reflecting step portions of the color filter patterns. Accordingly, when an alignment layer (not shown) is formed on the common electrode and rubbed, defects are caused near the step portions. Further, a cell gap between the array substrate and the color filter substrate is not uniform due to the step portions, and thus a margin of filling the liquid crystal between the two substrates is difficult to ensure.
Further, the common electrode is made of indium-tin-oxide having an amorphous state and has a thickness of angstroms. Accordingly, pigments of the color filter patterns may flow out through the common electrode 56, and thus the liquid crystal is contaminated by the pigments that flow out.